Printing systems are known in the art, such as for instance printers, photocopiers, fax machines, etc., that are suitable for producing the printout of a document by means of ink jet printing devices in the form of fixed or interchangeable printheads.
The composition and operating mode of an ink jet printing system are widely known to those acquainted with the art and a detailed description of one will not therefore be provided herein, but solely of some of the characteristics that are important for the understanding of this invention.
A typical jet printing system consists of:
1] Printing equipment comprising:
                a device for feeding and advancing a sheet of paper or other material (print medium) on which it is desired to print the image in such a way that the feeding takes place in a given direction in discrete steps (line feed);        a movable carriage sliding on guideways in a direction perpendicular to that of feeding of the sheet, actuated selectively by a motor so as to effect a forward motion and a return motion across the width of the sheet;        a printing device, for example a removable printhead, attached to the carriage, comprising multiple emission resistors deposited on a substrate (generally a plate of silicon) and arranged inside cells full of ink having corresponding nozzles, through which the head can emit droplets of ink having a given volume;        an electronic printing controller (print controller), connected to an electronic processor (computer), for exchanging information concerning printing data and settings and suitable for selectively controlling feeding of the sheet, movement of the carriage and activation of the printhead through the selective heating of the resistors and the emission of the ink droplets against the surface of the sheet; and2] A print management or print control software        this software, generally installed on the computer, cooperates with the print controller and is suitable for processing the original image to convert its original chromatic data into corresponding chromatic data for printing.        
In particular, the print driver is a program suitable for converting data relative to images and/or texts from a format generally made up of three distinct information planes R, G and B (Red, Green and Blue) for additive type systems, for instance cathode ray tubes, into a like number of distinct information planes C, M, Y and K (Cyan, Magenta, Yellow and Black) for subtractive type systems, for example printing systems.
The conversion of each image dot (pixel) from the RGB planes to the CMY and K planes, as is known, must take into account the level of intensity attributed to each pixel, a level which, as it is currently defined using 8 bits, may assume any binary value within a range of 256 intensity levels.
As is known, in order to also keep the intensity information in the conversion from RGB to CMY and K, the print driver associates a “superpixel” with each pixel consisting, for example, of a 16*16 dot matrix, representing the corresponding level of intensity to be obtained in the printing stage; accordingly, for example, 256 superpixels each representing a given intensity are associated by the print driver with the range of 256 levels of the pixel of one of the RGB planes.
As is known, each superpixel comprises white dots, representing the points at which not to eject ink, and black dots, representing the points at which to eject ink, and theoretically the number of black dots linearly corresponds to the level of intensity of the pixel; in practice, however, the print driver modifies the distribution of white and black dots in the superpixels on the basis of two correction factors:                the type of sheet or printing medium;        the print dot size.        
In actual fact, as can be understood by intuition, for like superpixels, the optical effect changes with changes in the type of medium and changes in the dot size.
One technical problem, common to all the ink jet printing systems, is that in order to keep the printing characteristics or quality constant, understood as repeatability of the optical sensation generated by the printed document, it is necessary, for like type media, for the print driver to use the “real” dot size; this is not however easy to obtain as it is subject to percentage variations, even large scale, on account of the following factors:                In the case of printing systems using replaceable heads, the dot size is subject to variations because the volume of the drops ejected changes from head to head on account of the manufacturing spreads of the heads;        The dot size, moreover, is influenced by temperature of the surrounding environment as this conditions efficiency of the head and therefore the volume of the drops ejected;        The dot size, for like droplet volumes, is highly dependent on the type of printing medium and on changes in its characteristics since both the medium type and its characteristics can produce a different extension of the drops on the medium;        Finally, the dot size, in the sense of the ways the droplets penetrate the printing medium, is influenced by the ambient humidity and by the humidity absorbed by the medium.        
Since, as already stated earlier, it is precisely the dot size that print drivers use in order to process the image to be printed and obtain constant printing results over time, the known art tries to overcome the above-mentioned problems in many different ways:                By using heads whose “droplet volume” data is stored in the factory in an appropriate memory on board the head. This technique, as well as not completely resolving the problem, is also expensive and suitable for implementation only on highly complex printing systems;        By producing print drivers dependent on the type of printing medium. In this case, the user must inform the driver which family of printing medium type he is using (plain paper, coated paper, glazed paper, photographic, transparency) so as to take into account the different dot size obtained from the same droplet volume. However even in the same family of media, there exist significant differences in dot size, and even between different production lots of the same type of medium, so that this method too only partially solves the problem described.Naturally, if the print driver uses a dot size different from the “real” size to “correct” the superpixels and, as a result, the image, the printing characteristics obtained are in fact different each time as the operating conditions change.        
In the known art, therefore, to overcome the problem described above the trend is to implement “typical” configuration values, in terms of printing medium and dot size, on the print drivers, accepting variations of the quality when the operating conditions do not correspond to the “typical” values. Unfortunately however, the known art does not indicate sure devices and methods with which to obtain constant printing quality and accordingly either a quality that is dependent on the operating conditions is accepted or more expensive and sophisticated printing technologies are used when the printing quality must necessarily be constant, as for instance in biomedical applications.